The present invention relates generally to load sensing such as utilized in connection with apparatus for indicating the loads sustained by lines, cables and the like in cranes, derricks and similar equipment.
Heretofore, as disclosed in U.S. Pat. No. 3,999,427, issued Dec. 28, 1976, it has been generally known to utilize a load sensing unit for load indicating apparatus, in which a hydraulic load cell and an electronic load cell are mechanically interconnected in stacked relation into a single load sensing unit appropriately connectable between opposed members of the apparatus capable of relative movements towards each other under the applied load forces which subject the load cells to the action of compression forces.
More recently, such combined hydraulic-electronic units have also been publicly known wherein the units are arranged to be connected between opposed members of the load indicating apparatus, that are movable away from each other under applied load tension forces.
For a number of years, many field installations have utilized load indicating apparatus of the type disclosed in U.S. Pat. No. 3,004,558, issued Oct. 17, 1961, in which the sensing device is of the hydraulic type and is in the form of a single unit that is pivotally connectable respectively at its upper and lower ends between a pair of opposed force applying members that are operable to subject the sensing device to tension forces.
Since the advent of the combined hydraulic-electronic sensing device concept, such as disclosed in the previously mentioned U.S. Pat. No. 3,999,427, the need has been realized for an improved combined hydraulic-electronic load sensing arrangement which would permit the utilization of a hydraulic sensing unit of the type disclosed in the above mentioned U.S. Pat. No. 3,004,558, and to which, in either a new indicating apparatus or an existing indicating apparatus in a field installation, an electronic sensing unit could be added in such a way as to be responsive to the same load forces as those applied to the associated hydraulic unit.
In the present invention this need has been fulfilled by the utilization of a strain detecting load cell embodiment of the type disclosed in U.S. Pat. No. 3,695,096, issued Oct. 3, 1972, in which the electronic unit takes the form of a coupling pivot pin structure, and which may be utilized to replace either the upper or lower pivotal connection for connecting the hydraulic unit with the load responsive members of the indicating apparatus. In the present disclosure, it is shown as replacing the pivot pin of the lower pivotal connection.
Since the load indicating signal of the coupling pivot pin type of load cell varies with the radial angle of application of the load forces, it is necessary to fixedly circumferentially orient the device with respect to a predetermined load application axis. For this purpose, there is provided a unique tool in the form of an elongated link member having the same length between its pivotally connected opposite ends as the hydraulic load sensing unit, and which is temporarily installed between the force applying members of the load indicating apparatus. The electronic coupling pin unit is utilized for one of the pivotal connections of the tool, and the associated tool end is provided with a shoulder portion for initial engagement with an anchor bar in a manner to initially position the bar in interfaced relation with a surface of the electronic sensing unit and to thereby position the unit in its proper operating position against rotation. The oriented position of the unit thus being determined, the anchor bar is then permanently welded or otherwise fixed to an adjacent portion of the associated force applying member. The tool is then removed and the hydraulic sensing unit installed, utilizing the thus oriented electronic unit as one of the pivot members.